Model depicting the role of the Erlin1/2-B12 interaction during SV40 ER membrane penetration.

<p>The Erlin1 and Erlin2 (Erlin1/2) complex is identified as a binding partner of B12. When SV40 traffics from the cell surface to the ER, it triggers the release of B12 from the Erlin1/2 complex (step 1). The released B12 in turn mobilizes to the foci (step 2) where B12 promotes ER-to-cytosol membrane penetration of SV40 by recruiting a cytosolic extraction complex [<a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1006439#ppat.1006439.ref006" target="_blank">6</a>,<a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1006439#ppat.1006439.ref021" target="_blank">21</a>] that ejects the virus into the cytosol. In the absence of the Erlin1/2 complex, B12 can mislocalize to the nucleus, suggesting that Erlin1/2 acts to anchor B12 in the ER.